Descartes’ Principles of Philosophy (Principia philosophiae) was the last of his three main expositions of his metaphysics and epistemology (or ‘first philosophy’, as he preferred to call it), and it was published in 1644. Unlike the Discourse on the Method, it was directed at a university audience, and was written in Latin. Unlike the Meditations on First Philosophy, it was directed towards the Faculty of Arts, rather than the Faculty of Theology. Students followed a general Arts course before proceeding to one of the ‘higher’ faculties, such as Theology or Law, and the syllabus included metaphysics and physics, based mainly on the works of Aristotle. Descartes’ ambition was that his book should replace Aristotle as the main text. It is therefore written in a rather more systematic and didactic style than his earlier works.

Remember that in the 17th century, the term ‘philosophy’ covered natural science as well as philosophy in the modern sense, and there is often no sharp divide between the two. I have selected the bits which are philosophically most relevant. The rest is largely quite technical, apriori theorising about cosmology, astronomy, physics, chemistry, and physiology.

Descartes intended the work to have six parts:

In fact he completed only the first four parts, and the concluding paragraphs of Part IV are a foretaste of what he would have written in the remaining two parts.

I have included the whole of Part I, the very beginning of Part II, one paragraph from Part III, and the end of Part IV.

The Principles of Philosophy was translated into French by Abbé Claude Picot, and published in 1647. Descartes gave the translation his warm approval; but we don’t know how carefully he vetted it; or whether he himself was responsible for any of the changes; or whether he considered them absolute improvements, or merely more suitable for a different audience. The changes are quite numerous, and it makes it difficult to read the text if all the variants are included. I have therefore translated from the Latin version, and only occasionally alluded to the French where relevant. It is also worth noting that most subsequent philosophers up to and including Kant would probably have read the work in the Latin version.

The standard edition (which I have used) is that of Charles Adam and Paul Tannery, Oeuvres de Descartes (revised edition: Paris, Vrin, 1964–76). The Latin original is in Vol. 8, Pt 1, and the French translation is in Vol. 4.

On difficult passages, I have compared my rendering with some of the more widely available previous English translations: